It is desirable that fire resistant windows meet the following requirements:                1. Optical clarity        2. Does not emit smoke when exposed to fire        3. Does not emit toxic fumes when exposed to fire        4. The windows can withstand jarring shocks when mounted in doors.        5. Prevents the transfer of heat to the opposite side of the flame.        
Recent prior art attempts to make fire resistant windows have been to provide a liquid medium or gel between fire resistant glass or polymer sheets.
Earlier prior art describes many versions of fire resistant windows. The initial ones were those with imbedded wire in glass. These were unsatisfactory due to breakage under high heat conditions and general overall loss of total transparency due to presence of wire, but there was nothing better. Subsequently fire resistant windows were developed which were formed with the actual window body having the outside glass panes and then a mixture of acrylamide and water with a catalyst were poured into the cavity between the panes of glass and the acrylamide allowed to polymerize forming a stable water gel.
This was a messy process subject to high unit losses during manufacturing. The performance of these units was usually adequate up to 30-40 minutes. Longer times could be achieved, but required significant increases in thickness and weight which is not acceptable. The steam formed by these units when subjected to high heat would immediately blow out the front glass pane. The resulting black char provided reasonable fire and thermal resistance. The subsequent development of gels formed from aluminum phosphate and optionally with borates was an improvement because the toxic acrylamide monomer was not involved. However, these gels took up to 24 hours to form and set in the window mold which was also not desirable and makes for high unit losses during manufacturing. In addition, the high water content of these systems causes the window to fail more rapidly due to the vast amounts of steam (from the contained water in the gel formed during direct flame impingement). The steam pressure actually blow out the front glass panes and even the back panes. Again, this happens in both the cases of the polyacrylamide and aluminum phosphate gels with water. In addition, these gels usually contain a sufficient amount of organic material to promote the gel formation which tends to carbonize during the flame impingement. The organic compounds usually convert to carbon foam which absorbs heat and reradiates heat (emissivity) as intumescent coatings do. However, this is not as efficient as direct reflectivity of the heat by a white body in cooling the back side of the window. There have been many fire window developments using castable compositions based on aluminum phosphates with the addition of diethanol amine and monoalkanol amines which after casting slowly hardens over 24 hours. All of these contain a significant amount of water which is undesirable in that the steam pressure is so great during fire impingement that the failure mode tends to be the blasting away of the front glass pane and possible the back ones depending on the window construction. Although the intumescent layer may hold in place, it is weak and is easily pushed aside in the fire hose test.
High temperature glasses have been developed based on lithium and alumina silicates which are difficult to manufacture and expensive in general and are difficult to make in sizes larger than 30″ wide. These are still limited in that they also still melt slowly at the temperature of the required testing and therefore still have difficulty meeting the one hour 900° C. flame test for 1 hour and do not insulate the back pane of the window causing excessive heat transfer. In addition, the haze levels are higher than standard window panes (reduced transparency).
What is needed for further improvement in the performance of fire windows is a hot castable, optically clear non flammable layer which does not melt when subjected to 900° C. flame (as glass does) and contains a low percentage water (<15%). It is preferred that it forms a white foam when subjected to an intense flame which is stable, insulative, and maintains a reflective white foam layer and has a relatively low water content (<15%) to minimize steam formation during this process. The composition must pour at a higher temperature (with low water content which is low enough to avoid kicking over to the white foam (intumesce), and yet when cooled to room temperature or in the hot sun does not melt. It is preferred that it immediately hardens as it is cast for east of manufacture and is ready to laminate. Post drying is satisfactory as long as the unit maintains its properties which are non-flammable, low water, optically clear and good impact resistance.
U.S. Pat. No. 4,264,681 to Girard et al, relates to fire resistant windows having spaces filled with an aqueous gel consisting of organic titanates, organic zirconates and silanes. The gel tends to bubble under jarring shock.
Fierch application Ser. No. 76/09227 discloses a fire resistant window wherein the intermediate gap between panes is filled with a gel that foams under extreme heat and contains mineral salts which causes a loss in optical clarity.
U.S. Pat. No. 5,449,560 to Antheunis relates to liquid curable compositions prepared from polydiorganosiloxanes and polyhydrogen organosilanes as an interlayer for a laminate of glass.
U.S. Pat. No. 5,124,208 to Bolton et al, which is herein incorporated by reference relates to a window assembly which can be used by the present invention.
Other fire resistant windows of interest include U.S. Pat. Nos. 7,090,906; 6,159,606; 5,885,713; 5,543,230 and 5,696,288 which are herein incorporated by reference.